|-USER------|
  | id        | (a unique identifier for the row)
  | views     | (count of how many pages user has viewed)
  | last_ip   | (the last IP address user used)
  | last_time | (the last time we saw the user)
  | url       | (the user's URL)
  |-----------|

##</code><code>##

  |-ALLIP-----|
  | id        | (a unique identifier for the row)
  | user_id   | (the id of the user that used this IP)
  | ip        | (the IP address)
  | time      | (the time it was seen)
  |-----------|

##</code><code>##

my $sql = <<SQLCODE;
  SELECT
    a.ip
  FROM
    ALLIP a,
    USER u
  WHERE
    a.user_id = u.id AND
    u.id = ?
  GROUP BY
    a.ip
SQLCODE

my $sth = $dbh->prepare( $sql );
if ( $sth && $sth->execute( $user_id ) )
{
    while ( my $row = $sth->fetchrow_arrayref() )
    {
        print( "IP address " . $row->[0] . "\n" );
    }
    $sth->finish();
}
else
{
    die( "Database error " . $dbh->errstr . "\n" );
}

##</code><code>##

my $found_id = undef;
my $sql = <<SQLCODE
  SELECT id
  FROM track 
  WHERE url = ?
SQLCODE

my $sth = $dbh->prepare( $sql );
if ( $sth && $sth->execute( $url ) )
{
    if ( my $row = $sth->fetchrow_arrayref() )
    {
        $found_id = $row->[0];
    }
}
else
{
    die( "Database error " . $dbh->errstr . "\n" );
}

if ( $found_id )
{
    # perform update
    $sql = <<SQLCODE;
  UPDATE user SET
    view = view + 1,
    last_ip = ?,
    last_time = ?
  WHERE
    id = ?
SQLCODE

    my $sth = $dbh->prepare( $sql );
    if ( $sth && $sth->execute( $last_ip, time(), $found_id ) )
    {
        if ( my $row = $sth->fetchrow_arrayref() )
        {
            $found_id = $row->[0];
        }
    }
    else
    {
        die( "Database error " . $dbh->errstr . "\n" );
    }
}
else
{
    # perform insert
    # code left to read as an exercise
}